Tail light cover

I have a 2003 Ram 1500. My neighbor knocked into it awhile ago but didn’t do any damage. However, one day I came out and the plastic lens that fits over all the taillights had fallen off. Fortunately it came off at home and not on the road somewhere. I’m wanting to know how to put it back on so that it stays. It almost looks like it just wedges into the channels around the edge, but I don’t want to stick it in there only to have it fall off on the road and lose it. It doesn’t seem to have had any glue or adhesive on it. Does anyone know what holds it in place?